1. Field of the Invention
The present invention relates to an image forming apparatus and a printing system that may form images on a recording medium with an adjustable image quality. The present invention also relates to an image adjusting method and a non-transitory computer-readable storage medium that stores a program for causing a computer to form images on the recording medium with the adjustable image quality.
2. Description of the Related Art
An image forming apparatus, such as a printing apparatus, a copying apparatus, a facsimile apparatus, and MFP (Multi-Function Peripheral) that includes functions of at least two of such apparatus, are provided with an image forming function to form images on a sheet-shaped recording medium such as paper (or transfer sheet). The image forming apparatus is popularly used in office environments and the like. Recently, the image forming apparatus is also used in production printing environments, such as commercial printing environments and enterprise printing environments, in place of an offset printing apparatus, because of the flexibility to cope with small lots and the ability to perform variable printing in which variable data are printed on advertising mails (or direct mails), posters, flyers, and the like.
The image forming apparatus for production printing uses the electrophotography technique that is identical to that used by the image forming apparatus for office use, for example. However, because the printed material output from the image forming apparatus for production printing is often the commercial product, the image quality required of the image forming apparatus for production printing is often higher than that required of the image forming apparatus for office use.
However, the image quality may be affected by the kind of recording medium used, even under identical printing conditions. For example, the different kinds of recording media may include plain paper, glossy paper, matte paper, envelope paper, film, and paper or sheet having different thicknesses and/or different sizes.
For this reason, the image forming apparatus may be provided with a setting function to accept characteristic values (for example, weight of transfer sheet, size or transfer sheet, glossiness of transfer sheet, and the like) of the transfer sheet from a user and to automatically set an image forming condition according to the characteristic values. An example of such an image forming apparatus is proposed in a Japanese Laid-Open Patent Publication No. 2006-276473. However, this proposed image forming apparatus may only cope with a general transfer sheet which is only one of a very large number of kinds of transfer sheets, and an optimum image formation may not be possible depending on the characteristic of the transfer sheet that is actually used. In this case, the image forming condition may be adjusted depending on the kind of transfer sheet that is actually used, but it requires complex management in order to manage combinations of the characteristic values and the image forming condition for each kind of transfer sheet.
In order to maintain the image quality of the printed material constant regardless of the kind of transfer sheet, the manufacturer of the image forming apparatus may investigate the characteristics, such as the toner adhesive property, for each transfer sheet to find an optimum image forming condition to be set in the image forming apparatus. However, the operation to find the optimum image forming condition is too difficult for the user, unless the user is very familiar with the operation and performance of the image forming apparatus. Consequently, the operation to find the optimum image forming condition is in many cases performed by a CE (Customer Engineer) of the manufacturer who is familiar with the operation and performance of the image forming apparatus.
FIGS. 1A through 1C are diagrams for explaining an example of a test printing to adjust the image quality. FIG. 1A illustrates an example of a test printing related mainly to toner density and image quality. Eight regions illustrated in FIG. 1A are printed at different toner densities, and the CE of the manufacturer checks the toner densities and finds the image forming condition that may avoid inconsistencies, unevenness, bias or the like in the toner density. FIG. 1B illustrates an example of a test printing mainly to test a fusing characteristic of the toner. Each of blocks illustrated in FIG. 1B are printed by varying conditions that affect the fusing characteristic of the toner, and the CE scrapes or scratches the printed surface, for example, and finds the image forming condition that results in the optimum toner fusing characteristic. FIG. 1C illustrates an example of a test printing to print a shading or hatching at a certain density. The CE finds the image forming condition in order not to generate a white spot or dot (insufficient toner), a blur (excessive toner), stripe noise and the like on the shading or hatching in FIG. 1C.
The image forming condition may be stored in the image forming apparatus as a set data group in which set data such as a secondary transfer reference current, a fusing temperature, and a linear velocity correction value, are grouped. The image forming apparatus may read the set data group that is set for each transfer sheet, and perform the printing to realize an optimum image quality based on the set data group.
However, the number of kinds of transfer sheets on the market is increasing, and it is becoming more and more difficult for the CE to cope with the individual transfer sheet. Hence, a Japanese Laid-Open Patent Publication No. 2008-102261 proposes an image forming system in which a relationship between the kind of transfer sheet and the set data group is stored in a server. According to this proposed image forming system, the image forming apparatus stores the set data group for each transfer sheet in the server that is connected to the image forming apparatus via a communication line, and the set data group is automatically set in the image forming apparatus from the server when the user selects the kind of transfer sheet. But in this case, the CE who is an expert on the image forming apparatus must manually add the combination of the kind of transfer sheet and the set data group when increasing the number of combinations of the kind of transfer sheet and the set data group stored in the server. For this reason, it is difficult from the practical point of view to cope with the number of kinds of transfer sheets that may increase on a day to day basis.
When the kind of transfer sheet desired by the user is not stored in the server, the Japanese Laid-Open Patent Publication No. 2008-102261 also proposes forming images on the desired kind of transfer sheet using a testing set data group for testing. In this case, the printed material output from the image forming apparatus may be read by an image reading apparatus, such as a scanner, in order to find the optimum set data group. The user may acquire the set data with respect to the kind of transfer sheet not stored in the server by performing a relatively easy procedure described above.
However, a satisfactory image quality may not be guaranteed using the set data group that is created using only the information acquired from the image reading apparatus, with respect to the user who requires a relatively high image quality. In this case, the CE who is specialized in evaluating the transfer sheet needs to evaluate the transfer sheet and determine the set data group based on the evaluation result.
For example, a Japanese Laid-Open Patent Publication No. 2009-271139 proposes a technique to evaluate the transfer sheet by an expert institution and to reflect the evaluation result in the server within a relatively short time. According to this proposed technique, the server that connected to the image forming apparatus is connected to a remote transfer sheet managing system via a communication line, and the evaluation result of the transfer sheet from the expert institution is reflected to the server.
However, according to the techniques proposed in the Japanese Laid-Open Patent Publications No. 2008-102261 and No. 2009-271139, the server must centrally manage the set data group for all of the kinds of transfer sheet. In addition, even when the user is unsatisfied with the image quality obtainable by the set data group managed by the server with respect to a certain kind of transfer sheet, the user may not modify the set data group stored with respect to this certain kind of transfer sheet. In other words, when a plurality of users are using the same kind of transfer sheet and one user is unsatisfied with the image quality obtainable using the set data group managed in the server with respect to the transfer sheet, while the other users are satisfied with the image quality, and the one user modifies the set data group with respect to the transfer sheet to obtain the image quality satisfactory to the one user, this image quality satisfactory to the one user may be unsatisfactory to the other users.
In order to enable all of the users to obtain the satisfactory image quality in the above described case, the server needs to manage the relationship between the kinds of transfer sheets and the set data group for each of the users. That is, the server needs to manage a number of set data groups corresponding to a product of the number of kinds of transfer sheets and the number of users. Consequently, the amount of data to be managed in the server becomes extremely large as the number of kinds of transfer sheets and/or the number of users increase, to thereby make the system operation difficult from the practical point of view.